1. Field of the Invention
This invention relates to a radiation image read-out apparatus for use in a radiation image recording and reproducing system. This invention particularly relates to a radiation image read-out apparatus wherein image read-out from a stimulable phosphor sheet carrying a radiation image stored thereon in the form housed in a cassette is conducted without taking the stimulable phosphor sheet out of the cassette. This invention also relates to a cassette for use in the radiation image read-out apparatus.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet or simply as a sheet) is first exposed to a radiation passing through an object to have a radiation image of the object stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, and the radiation image of the object is reproduced as a visible image by use of the image signal on a recording material such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
In the aforesaid radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store a radiation image until the sheet is scanned with stimulating rays for reading out the radiation image. Therefore, after the radiation image is read out from the stimulable phosphor sheet, radiation energy remaining thereon should be erased to reuse the sheet. For satisfying this requirement, it has been proposed to provide a radiation image read-out apparatus with a read-out section for reading out an image stored on a stimulable phosphor sheet, and an erasing section for erasing radiation energy remaining on the sheet.
To the proposed radiation image read-out apparatus, a stimulable phosphor sheet housed in a cassette and subjected to image recording by use of an external image recording apparatus is fed in the form housed in the cassette. When the cassette housing the sheet carrying a radiation image stored thereon is fed to the read-out apparatus, the sheet is taken out of the cassette in the read-out apparatus and transferred to a sheet conveyance means for conveying the sheet to the read-out section for conducting image read-out.
In the conventional radiation image read-out apparatus, the taking-out of the sheet from the cassette is generally done by opening a cover member of the cassette, which is openably mounted on a cassette body housing the sheet and is parallel to the sheet surface, by an opening member provided in the read-out apparatus, and then taking the sheet out of the cassette body and transferring it to the adjacent sheet conveyance means by use of a suction means. However, in order to conduct the taking-out of the sheet in this manner, it is necessary to provide the suction means for sucking up the sheet and transferring the sheet to the sheet conveyance means, and the mechanism of the apparatus becomes complicated. Also, since it is necessary to provide the apparatus with a space for opening and closing of the cover member of the cassette and a space for moving the suction means, a problem of the apparatus becoming large arises. Further, since the sheet is taken out of the cassette by being sucked up by the suction means and conveyed in the apparatus by being gripped between rollers, belts or the like, the sheet is readily scratched or damaged, and the service life of the sheet becomes short.